Fusion is a developmental anomaly of dental hard tissues. Most cases occur in the anterior region of both the primary and permanent dentitions. Occasionally, fusion of permanent and supernumerary teeth may occur in the maxillary anterior region; however, a supernumerary tooth fused with a premolar is a rare case. Developmental lateral periodontal cyst is also an uncommon developmental odontogenic cyst with no clinical symptoms, and the lesion is often discovered on routine radiographic examination. In the present case, we report the uncommon fusion of teeth and lateral periodontal cyst in a Chinese girl. Using cone beam computed tomography we are able to acquire a better understanding of the complicated root canal morphology of the fused tooth and successfully manage the lateral periodontal cyst. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011; 112: e18-e20)